Ethyl 3-Bromopropiolate: Properties, Uses & Handling FAQ

Ethyl 3-bromopropiolate is an activated, electrophilic bromoalkyne ester widely used in organic synthesis as a versatile building block for cross-coupling reactions, cycloadditions, and the preparation of functionalized alkynes.

Chemical Name

Ethyl 3-bromopropiolate

Molecular Formula

C5H5BrO2

Molecular Weight

177.00 g/mol

CAS Number

4620-73-9

Functional Groups

Terminal bromoalkyne and ester (ethyl ester)

Key Reactivity

Electrophilic alkyne suitable for nucleophilic addition, Sonogashira coupling, and [2+2]/[3+2] cycloadditions

Storage

Store in a cool, dry place away from light; refrigeration recommended

What Is Ethyl 3-Bromopropiolate and What Are Its Key Properties?

Ethyl 3-bromopropiolate (CAS 4620-73-9; molecular formula C₅H₅BrO₂; MW ≈ 177.00 g/mol) is a bromine-substituted propiolic acid ethyl ester. The molecule combines two strongly electron-withdrawing features: a carbon–carbon triple bond (alkyne) and a conjugated ester group, flanked by a C–Br bond at the terminal alkyne carbon. This arrangement creates a highly electrophilic, activated alkyne system.

The compound is typically a pale-yellow liquid at room temperature. The ester moiety lowers the electron density of the triple bond, making it substantially more reactive toward nucleophiles and cycloaddition partners than unactivated alkynes. The carbon–bromine bond simultaneously provides a handle for metal-catalysed cross-coupling chemistry.

What Are the Main Synthetic Applications of Ethyl 3-Bromopropiolate?

Ethyl 3-bromopropiolate serves multiple roles in synthetic organic chemistry:

• Sonogashira-type and other metal-catalysed cross-coupling reactions: The C–Br bond undergoes oxidative addition to palladium(0) and copper catalysts, enabling the installation of diverse aryl, heteroaryl, or vinyl groups to produce internal alkynoates.
• Cycloaddition reactions: The activated triple bond participates as a dienophile or dipolarophile in [4+2] Diels–Alder and [3+2] 1,3-dipolar cycloadditions, yielding heterocyclic and carbocyclic products with an ester handle for further elaboration.
• Nucleophilic addition: Amines, thiols, and other soft nucleophiles add across the activated triple bond, generating vinyl bromide adducts useful as masked electrophiles or cross-coupling partners.
• Click and multicomponent reactions: The compound has been employed in multicomponent strategies where both the bromo substituent and the ester provide orthogonal sites for further functionalisation.

These properties make ethyl 3-bromopropiolate a versatile two-directional building block for the rapid assembly of complex molecular scaffolds.

How Should Ethyl 3-Bromopropiolate Be Stored and Handled Safely?

Storage: Store ethyl 3-bromopropiolate in a tightly sealed container under inert atmosphere (nitrogen or argon) in a cool, dark location. Refrigeration (2–8 °C) is recommended to minimise decomposition. Protect from moisture, light, and heat. Check the vial for discolouration or particulates before use; discard if significant degradation is apparent.

Safe handling: Ethyl 3-bromopropiolate is an irritant and potential lachrymator due to the reactive electrophilic alkyne. Always work in a well-ventilated fume hood. Wear appropriate personal protective equipment including nitrile gloves, laboratory coat, and safety glasses. Avoid inhalation of vapours and contact with skin or eyes.

Waste disposal: Dispose of waste in accordance with local regulations for halogenated organic solvents and reagents. Do not pour down the drain.

Note: Always consult the current Safety Data Sheet (SDS) provided by Aladdin Scientific for authoritative hazard information specific to your lot.

What Reaction Conditions Are Typically Used with Ethyl 3-Bromopropiolate?

Reaction conditions vary depending on the transformation:

• Sonogashira coupling: Typically employs a Pd(0)/Cu(I) co-catalyst system (e.g., Pd(PPh₃)₄ or Pd(OAc)₂/PPh₃ with CuI), an amine base (triethylamine or diisopropylamine) as solvent or co-solvent, under inert atmosphere at room temperature to 60 °C. Ethyl 3-bromopropiolate acts as the electrophilic coupling partner rather than the terminal alkyne component.
• Cycloadditions: Often performed without metal catalysts, in organic solvents such as toluene, dichloromethane, or THF, at temperatures ranging from –20 °C to reflux, depending on the reactivity of the diene or dipole partner.
• Nucleophilic thiol or amine additions: Typically conducted at 0 °C to room temperature in polar aprotic or protic solvents with a mild base, yielding vinyl bromide products with defined geometry.

Because the compound is sensitive to nucleophilic attack and moisture, reactions should be set up under anhydrous, inert conditions wherever possible. Titration of the reagent concentration prior to use may be advisable for sensitive applications.

Quality, Purity and Ordering Information

Aladdin Scientific offers ethyl 3-bromopropiolate (SKU: E725537) for research use. The reagent is characterised by standard analytical techniques including GC purity assessment and NMR verification. Researchers should request the Certificate of Analysis (CoA) for lot-specific purity data and confirm suitability for their application.

For bulk quantities, custom packaging, or special purity requirements, contact Aladdin Scientific's technical sales team. Reward points, promotional pricing, and volume discounts may be available; consult current promotions on the Aladdin Scientific website or contact customer service.

Ethyl 3-bromopropiolate is intended for research and development purposes only and is not suitable for drug, food, or household use.

Frequently asked questions

What is ethyl 3-bromopropiolate used for in organic synthesis?

Ethyl 3-bromopropiolate is used primarily as an electrophilic alkyne building block. It participates in palladium/copper-catalysed cross-coupling reactions (acting as the halide partner), Diels–Alder and 1,3-dipolar cycloadditions, and nucleophilic addition reactions with amines or thiols to give vinyl bromide adducts for further elaboration.

How does ethyl 3-bromopropiolate differ from ethyl propiolate?

Ethyl propiolate contains a terminal C–H alkyne, making it suitable as the nucleophilic (terminal alkyne) partner in Sonogashira couplings. Ethyl 3-bromopropiolate replaces that terminal hydrogen with bromine, converting it into an electrophilic coupling partner. The C–Br bond also provides steric and electronic differences that alter cycloaddition regioselectivity and enable reactions not accessible with the parent propiolate.

Is ethyl 3-bromopropiolate sensitive to moisture or air?

Ethyl 3-bromopropiolate is moderately sensitive to moisture and should be handled under inert conditions. The activated ester and electrophilic alkyne can undergo hydrolysis or slow decomposition upon prolonged exposure to air and moisture. Store under inert gas in a sealed container at 2–8 °C and use freshly opened material for best results.

What solvents are compatible with ethyl 3-bromopropiolate?

Common compatible solvents include dichloromethane, tetrahydrofuran (THF), toluene, acetonitrile, and dimethylformamide (DMF). Highly nucleophilic or protic solvents (e.g., water, methanol) should generally be avoided unless nucleophilic addition is the intended transformation, as they may react with or decompose the reagent.

Where can I purchase ethyl 3-bromopropiolate and what SKU should I use?

Ethyl 3-bromopropiolate is available from Aladdin Scientific under SKU E725537. Place your order through the Aladdin Scientific website or contact customer service for pricing, availability, volume discounts, and shipping options. Always quote the SKU to ensure you receive the correct product.

References

1. Sonogashira, K. Development of Pd–Cu catalyzed cross-coupling of terminal acetylenes with sp2-carbon halides. Journal of Organometallic Chemistry, 2002, 653(1–2), 46–49. doi:10.1016/S0022-328X(02)01158-0
2. Brandsma, L. Preparative Acetylenic Chemistry, 2nd ed.; Elsevier: Amsterdam, 1988. General reference for bromoalkyne preparation and reactivity.
3. Himeshima, Y.; Sonoda, T.; Kobayashi, H. Fluoride-induced 1,2-elimination of o-trimethylsilylphenyl triflate to benzyne under mild conditions. Chemistry Letters, 1983, 12(8), 1211–1214. (General reference for activated alkyne cycloadditions)

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.